The present invention relates to a method and apparatus for controlling the traversing frequency in a yarn winding system, and in particular it relates to a method and apparatus for controlling the traversing frequency in a yarn winding system used in the production of yarn packages of synthetic fibers. More particularly, the invention relates to a method and apparatus for winding a yarn into a cross-wound package, and wherein the formation of undesirable ribbons is avoided.
When winding a yarn on a rotating tube, the yarn is constantly traversed along the length of the tube, so as to achieve a uniform distribution of the yarn on the tube, and to ensure a satisfactory strength of the yarn package being formed. The strength of the yarn package is of especially great importance for its transportation. The quality of traversing the yarn influences likewise the unwinding of the yarn package. In addition, the quality of the yarn package is rated by its wound structure.
During the winding, the traversing of the yarn is subjected to so-called laws of traverse. Basically, these laws of traverse distinguish between a random wind and a precision wind. In a random wind, the yarn is traversed substantially at a constant frequency, while it is being wound, which leads at a substantially constant speed of the advancing yarn to constant angles, at which the yarn is deposited on the package. In a precision wind, the frequency of the reciprocating movement (traverse) is tied to the speed of the package which slows down continuously during the winding process at a constant speed of the advancing yarn.
For many applications, the random wind is preferred because of the constant angle at which the yarn is deposited. However, the random wind has the disadvantage that so-called ribbons or patterns form during the winding operation. Ribbons will develop, when the ratio of the package speed to the traversing frequency results in an integer. Since the speed of the package decreases continuously during the winding process, such a condition may occur several times during the winding operation. As a result of the integral ratio of the frequencies, the yarn traversing mechanism deposits the yarn over several rotations of the package in the same location, i.e., over several rotations the advancing yarn comes to lie directly above the just previously wound yarn, and then slips off toward one side. This leads to a disorderly winding of the yarn, and is as such an undesired behavior.
Methods of winding a yarn to a cross-wound package are disclosed in U.S. Pat. Nos. 4,504,024 and 4,697,753. Both methods serve to avoid critical winding situations.
Critical winding situations include primarily those in which the spindle speed and the traversing frequency form an integral ratio or a ratio broken by a small integer. These situations are named pattern or "ribbon" formation. A so-called ribbon represents not only a major interference with the package buildup, but may also lead to an interruption of the winding process and to a destruction of the takeup machine by occurring imbalances.
It has shown that even in the case of a nonintegral wind ratio or wind ratios, which are not broken by a small integer (2, 3, 4 . . . ), ribbon situations or ribbon-like situations may still occur. These situations are in part process-dependent and unforeseeable. To avoid the ribbon formation in the first-mentioned case, the traversing motion is controlled in particular as a function of the wind ratios which occur during the winding of a cross-wound package. In this instance, they represent so-called "ribbon values", which announce their arrival by the ratio of spindle speed to traversing frequency. In the second case, it is a control of the traversing motion as a function of a predetermined traversing program.
In the simplest case, such a traversing program includes a predetermined traversing speed. Such a predetermined traversing speed may also be superposed by fluctuations (wobbling). In the method disclosed in U.S. Pat. No. 4,697,753, the traversing speed does not remain constant, but varies between an upper limit and a lower limit in accordance with a predetermined regularity, it being likewise possible that the upper limit and the lower limit change during the winding of a cross-wound package (winding cycle).
Described in BARMAG Publication No. 31 (9/1991), pp. 36-38, are several methods of avoiding ribbon formations. In a method described as ribbonfree random winding, the ribbons are skipped or jumped by switching the traversing frequency. Intermediate ribbons may be bypassed only by an additional wobbling. In a wobbling, the traversing frequency fluctuates about a mean traversing frequency.
In the described methods, the instant and the height of the jump are calculated from the ratio of speed to traversing frequency. Since the negative effects of a ribbon show not only at an exactly integral ratio, but also in a region outside the exactly integral ratio, the calculation of the time to jump requires that an adequate distance from the ribbon be assured. However, because of the continuously decreasing package speed and because of the fact that the builds of two packages are never identical, the calculated time of the jump frequently does not coincide with an optimal time of the jump.
It is therefore the object of the present invention to provide a method and apparatus for controlling the traversing frequency and possibly other parameters of the winding process, which allows undesired winding situations that are to be expected in the course of a winding process to be reliably avoided.